The present invention relates to a system and method for cleaning a hot coal-derived fuel gas. More specifically, the present invention relates to a hot gas cleanup system and a method for removing particulates, sulfur and alkali species from high temperature, high pressure coal-derived fuel gas in an integrated combined cycle coal gasification power plant or in a direct coal-fired gas turbine power plant.
The high efficiency, low capital cost and short lead time of gas turbine based power plants make them particularly attractive to electric utilities as a means of producing electrical power. Unfortunately, traditionally, gas turbines have been limited to operation on expensive, sometimes scarce, fuels--chiefly, distillate oil and natural gas. As a result of the ready availability and low cost of coal, considerable effort has been expended toward developing a gas turbine system for generating electrical power that can utilize coal as its primary fuel.
Two such approaches have been developed. In one approach, referred to as an integrated combined cycle coal gasification power plant, steam and compressed air from the gas turbine compressor, or compressed oxygen, is used to partially combust coal in a gasifier to produce a low to medium heating value fuel gas. In the second approach, coal is directly gasified in compressed air from the compressor, producing a low heating value fuel gas. In either approach, a high temperature, high pressure gas is produced that must then be expanded in the turbine section of the gas turbine. Since the gas contains particulate matter, as well as sulfur and alkali species, all of which can be harmful to the turbine components, it is important that the gas be cleaned prior to expansion in the turbine. The cleaned gas should also satisfy environmental emission standards.
Traditionally, fuel gas cleanup systems operate at near ambient temperature and require large heat exchanger equipment to cool the hot fuel gas prior to cleaning. Such low temperature gas cleaning is expensive and reduces the power plant efficiency. While high temperature cleanup systems have been proposed that utilize ceramic barrier filter technology to remove particulates and zinc-based sorbents to remove sulfur, such systems have a high capital cost and are expensive to operate. The operating temperature of the zinc-based sorbents is limited so that large heat exchanger equipment is still required. In addition, the cost of zinc-based sorbents is high and sorbent losses due to physical and chemical attrition are great and has a significant negative impact on operating cost.
It is therefore desirable to provide a hot fuel gas cleanup system that is capable of operating on high temperature, high pressure fuel gas and in which the use of expensive sorbents is minimized, thereby making the system economical to operate.